Very slow coolant leak

[Paul297]

Hello everyone

Hoping someone can give me some pointers here...

Got my 2014 C Class 250CDI last August. About a month after getting it, I had the coolant level warning. Topped it up with about 300ml, if that.

Looked this morning and it's a lot lower than it was. Not has the warning yet though.

Done only about 5000 miles since I topped it up. So 300ml in 5000 miles is very slow.

Any ideas what could be going off?

Thanks

 

[Jim2]

In mine, it was the fuel filter housing...no visible water stains or leakage signs, but slow leak. Its a known problem with the OM651 CDI engine. The original filter housing is held in place with two bolts, and this allows the seal to warp causing the leak, The replacement housing has 3 bolts, and solved the problem. BTW, mine is a 2014 E class w212.

 

[steveq]

On mine it was the water pump.
The leak started off very slowly with a top up every month or two.
It slowly worsened over a number of months to requiring a top up every week.

The leak wasn't visible as the coolant evaporated off the hot engine. I looked for the leak with the engine running when it was cold and could see a seepage from the centre of the pump.

 

[ioweddie]

Plastic water pump

 

[steveq]

Plastic water pump

Yes, but it leaked out of the metal part !!

 

[M80]

Plastic water pump

Not only.
Are the pistons metal on the 651?

To the op, is there any sign of white smoke shortly after start up?

 

[LostKiwi]

Are the pistons metal on the 651?

Can't imagine what else they'd be (although MB have been known to use cheese for timing gears and chocolate for chains).

 

[steveq]

The full metal jacket water pump on my previous W211 E220 CDI failed at much the same age & mileage.

 

[Jim2]

On mine it was the water pump.
The leak started off very slowly with a top up every month or two.
It slowly worsened over a number of months to requiring a top up every week.

The leak wasn't visible as the coolant evaporated off the hot engine. I looked for the leak with the engine running when it was cold and could see a seepage from the centre of the pump.

Always good to find the leak culprit, caught in the act...

 

[Paul297]

Thanks for the replies and the entertainment

I had a look around the fuel filter housing today as best I could but couldn't see it anything. Tried to have a look at the water pump but couldn't get a view down the front.

How would you recommend trying to get a better look? Do I have to get underneath?

Also, I'm not overly mechanically savvy... but if I could just locate it before taking it to a garage, it might save me being taken for a ride. It is still under warranty, but I'd like to go in clued up.

Thanks again, really appreciated.

 

[Jim2]

Thanks for the replies and the entertainment

I had a look around the fuel filter housing today as best I could but couldn't see it anything. Tried to have a look at the water pump but couldn't get a view down the front.

How would you recommend trying to get a better look? Do I have to get underneath?

Also, I'm not overly mechanically savvy... but if I could just locate it before taking it to a garage, it might save me being taken for a ride. It is still under warranty, but I'd like to go in clued up.

Thanks again, really appreciated.

Of the two possibilities, the water pump will be the easier to spot. See Steveq's post above. For the fuel filter housing, its more difficult, as its harder to see, and when the car is moving, it tends to disperse the water, leaving no "Evidence ". But I'm pretty sure that the dealership will be more than capable of finding the exact cause as it's a pretty common fault in MB

 

[Exp21]

Hi, my w204 has had a new water pump. But coolant level keeps going down very slowly with mileage. I brought it back to the dealer after repairs and they did a pressure/leak test on coolant system telling it's all right. Honestly I think that or the leak is so little that it's not detectable in minutes with the pressure gauge, or there's a minor head gasket leak of coolant. Or it leaks from the reservoir cap that to me it seems not that "sealed".

Anyway they already told you where it could leak in OM651. I've heard of some rare cases of blown head gaskets, check also this aspect just to be more sure and exclude that

 

[Jim2]

The water pump and filter housing are generally the "usual suspects " but there's other possibilities too. Water getting into the engine ( creamy colored oil on the oil filler cap)or transmission fluid ( there was one type of atf cooling radiator which allowed antifreeze to pass from the main radiator and mix with the atf fluid). There are a lot of possibilities. Good luck with it, and keep updating, if you can.

 

[LostKiwi]

Add some UV dye to the coolant. Run around a few days then at night open the bonnet and shine the UV torch in. Any leaks that evaporate leaving no trail will leave the dye behind.

 

[Dean Fletcher]

Plus 1 for the water pump and fuel filter housing. Changed both on my om651. Watch out when changing the fuel filter housing as the (new and improved) housing now has 3 holes for a better fit. My car didnt have a place for the 3rd hole but I still managed to get it to fit tho. The part was bought through a Mercedes parts specialist who had my details aswell. If its the housing the seal will go and you will notice fluid build up next to the fuel filter easy seen with a light.

 

[steveq]

Thanks for the replies and the entertainment

I had a look around the fuel filter housing today as best I could but couldn't see it anything. Tried to have a look at the water pump but couldn't get a view down the front.

How would you recommend trying to get a better look? Do I have to get underneath?

Also, I'm not overly mechanically savvy... but if I could just locate it before taking it to a garage, it might save me being taken for a ride. It is still under warranty, but I'd like to go in clued up.

Thanks again, really appreciated.

To see the water pump you have to take off the big plastic air intake pipe that goes from the front grill to the air filter housing. Then you have to remove the cover in front of the engine. That pulls forwards and upwards. That exposes the serpentine belt and pulleys. The water pump is towards the left side.
The leak will be very slight and hard to see.
It will only occur when the engine is running but watch the little fingers!!

 

[Exp21]

Or if you have one use an endoscope. With that you can go into the smallest corners and check traces of coolant

 

[Dean Fletcher]

If possible take off the underside plastic tray and lay down some newspaper, let the car get up to temp and see if it drips is specific places. When my water pump went it started steaming from the from end as it was dripping on hot pipes.

 

[malcolm E53 AMG]

We had a new sprinter van at work that suffered a coolant leak turned out to be a porous hose of all things and very difficult to identify so the culprit could be anything including o ring seals nowadays